C# – How to Convert Value Type to byte[]

arraysc++

I want to do the equivalent of this:

byte[] byteArray;
enum commands : byte {one, two};
commands content = one;
byteArray = (byte*)&content;

yes, it's a byte now, but consider I want to change it in the future? how do I make byteArray contain content? (I don't care to copy it).

Best Answer

To convert any value types (not just primitive types) to byte arrays and vice versa:

    public T FromByteArray<T>(byte[] rawValue)
    {
        GCHandle handle = GCHandle.Alloc(rawValue, GCHandleType.Pinned);
        T structure = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(T));
        handle.Free();
        return structure;
    }

    public byte[] ToByteArray(object value, int maxLength)
    {
        int rawsize = Marshal.SizeOf(value);
        byte[] rawdata = new byte[rawsize];
        GCHandle handle =
            GCHandle.Alloc(rawdata,
            GCHandleType.Pinned);
        Marshal.StructureToPtr(value,
            handle.AddrOfPinnedObject(),
            false);
        handle.Free();
        if (maxLength < rawdata.Length) {
            byte[] temp = new byte[maxLength];
            Array.Copy(rawdata, temp, maxLength);
            return temp;
        } else {
            return rawdata;
        }
    }

Related Solutions

C# – Convert Array of Different Value Types to Byte Array

Well, you could have a map like this:

private static readonlyDictionary<Type, Func<object, byte[]>> Converters = 
    new Dictionary<Type, Func<object, byte[]>>()
{
    { typeof(string), o => Encoding.UTF8.GetBytes((string) o) },
    { typeof(bool), o => BitConverter.GetBytes((bool) o) },
    { typeof(char), o => BitConverter.GetBytes((char) o) },
    ...
};

public static void ToBytes(object[] data, byte[] buffer)
{
    int offset = 0;

    foreach (object obj in data)
    {
        if (obj == null)
        {
            // Or do whatever you want
            throw new ArgumentException("Unable to convert null values");
        }
        Func<object, byte[]> converter;
        if (!Converters.TryGetValue(obj.GetType(), out converter))
        {
            throw new ArgumentException("No converter for " + obj.GetType());
        }

        byte[] obytes = converter(obj);
        Buffer.BlockCopy(obytes, 0, buffer, offset, obytes.Length);
        offset += obytes.Length;
    }
}

You're still specifying the converter for each type, but it's a lot more compact than the if/else form.

There are various other ways of constructing the dictionary, btw. You could do it like this:

private static readonly Dictionary<Type, Func<object, byte[]>> Converters = 
        new Dictionary<Type, Func<object, byte[]>>();

static WhateverYourTypeIsCalled()
{
    AddConverter<string>(Encoding.UTF8.GetBytes);
    AddConverter<bool>(BitConverter.GetBytes);
    AddConverter<char>(BitConverter.GetBytes);
}

static void AddConverter<T>(Func<T, byte[]> converter)
{
    Converters.Add(typeof(T), x => converter((T) x));
}

I see another answer has suggested binary serialization. I'm personally not keen on "opaque" serialization schemes like that. I like to know exactly what's going to be in the data in a way that means I can port it to other platforms.

I would point out, however, that your current scheme doesn't give any sort of delimiter - if you have two strings, you'd have no idea where one stopped and the other started, for example. You also don't store the type information - that may be okay, but it may not be. The variable length issue is usually more important. You might consider using a length-prefix scheme, like the one in BinaryWriter. Indeed, BinaryWriter may well be a simpler solution in general. You'd probably want to still have a map of delegates, but make them actions taking a BinaryWriter and a value. You could then build the map by reflection, or just a hardcoded list of calls.

Then you'd just initialize a BinaryWriter wrapping a MemoryStream, write each value to it appropriately, then call ToArray on the MemoryStream to get the results.

C# – Converting int[] to byte[]

If you want a bitwise copy, i.e. get 4 bytes out of one int, then use Buffer.BlockCopy:

byte[] result = new byte[intArray.Length * sizeof(int)];
Buffer.BlockCopy(intArray, 0, result, 0, result.Length);

Don't use Array.Copy, because it will try to convert and not just copy. See the remarks on the MSDN page for more info.

Best Answer

Related Solutions

C# – Convert Array of Different Value Types to Byte Array

C# – Converting int[] to byte[]

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